The present invention relates to a servo steering gear mechanism having a servomotor to which a pressurized operating medium is conducted from an inlet port and from which the operating medium is returned through an outlet port to a low pressure reservoir.
A problem common to such servo steering gear mechanism is the development of unpleasant and disturbing noises of a hissing nature in response to attainment of a predetermined pressure level therein. Such noises arise by virtue of flow through valve controlled passages under a pressure differential. The noise level increases as the pressure differential increases. Since a sharp reduction in operating pressure occurs during flow through the return passage of the valve structure, the noise or hissing sounds become particularly disturbing at valve surfaces of the return flow passage. This problem is dealt with by the inventions as disclosed in prior copending application Ser. No. 68,363, filed Aug. 21, 1979 for Auxiliary Power Steering and in copending application Ser. No. 102,327, filed Dec. 11, 1979 for Rotary Slide Steering Valve For Auxiliary Power Steerings, said related copending applications being owned in common with the present application by the same assignee.
Heretofore, attempts have been made to improve pressure conditions in the return flow valve passages by volumetric accumulation of fluid. Any prolonged accumulation of fluid along the return flow path is, however, undesirable for steering gear mechanism having unbalanced pressure operated control valves because of a deterioration of steering return movement. Also, additional heating of the fluid operating medium occurs requiring the expenditure of more energy.
It is therefore an important object of the present invention to provide a servo steering gear mechanism of the aforementioned unbalanced type in which return flow pressure conditions are improved to reduce the hissing noise level without fluid accumulation.